An integrated series of structural and functional studies of frog retinal rod outer segment (ROS) photoreceptors and isolated disk membranes are proposed. The absolute mass concentrations of water and total solids in the ROS per lamellar repeat will be established by coordinated isopycnic density centriguation, x-ray diffraction and x-ray absorption techniques. This concentrations of water and solids per lamellar repeat will be experimentally correlated with the bulk refractive index of the ROS. Contribution of form birefringence effects to the ROS axial birefringence gradient will be examined by determining the lamellar repeat period and disk membrane pair spacing as functions of position along the ROS axis. Primary magnification x-ray absorption studies of individual ROSs will be carried out on a conventional x-ray microscope to see if there is a gradient in total mass concentration along the ROS axis. Such studies will be coordinated with polarization microscopic observations. Efforts to increase the domain size of the 2-dimensional crystalline arrays induced thusfar in negatively stained disk membranes will be continued. X-ray and freeze-fracture studies of isolated frog ROS lipids are aimed in particular at understanding the small paracrystalline inclusion of hexagonal II lipid phases in ROSs. Correlated room temperature and low-temperature (LN2) x-ray scattering studies, together with freeze-fracture studies of isolated ROSs, will further elucidate the structural significance of disk membrane freeze-fracture textures.